Catherine Margaret Ashton was born on 20 March 1956 in Upholland, Lancashire, the daughter of Harold and Clare Margaret Ashton. She was educated at Upholland Grammar School, Wigan Mining and Technical College, and Bedford College, University of London. She married Peter Kellner in 1988 and she has two children and three step-children.

She worked for the Campaign for Nuclear Disarmament, 1977-9; the Coverdale Organisation, 1979-81; and the Central Council for Education and Training in Social Work. She was the director of Business in the Community, 1983-9, before becoming a freelance policy adviser, 1989-99. She also chaired the Hertfordshire Health Authority, 1998-2001, and was vice-president of the National Council for One-Parent Families.

She was created a life peer as Baroness Ashton of Upholland in 1999 and served in the Labour government as Parliamentary Under-Secretary of State in the Department for Education and Skills, 2001-4, and the Department for Constitutional Affairs (later the Ministry of Justice), 2004-7. She became a member of the Privy Council, in 2006, and joined the Cabinet as Leader of the House of Lords and Lord President of the Council, 2007-8.

In 2008, she was nominated by the UK as the European Commissioner for Trade. She then became the European Union's first High Representative for Foreign Affairs and Security Policy, 2009-14, and Vice-President of the European Commission, 2010-14, in which roles she established and led the European External Action Service. Notable diplomatic achievements during this period included negotiations to normalise relations between Serbia and Kosovo and to reach an interim agreement with Iran over its nuclear programme.

She is Chancellor of the Most Distinguished Order of St Michael and St George and a Lady Companion of the Order of the Garter.

Her publications include: 'And Then What? Inside Stories of 21st Century Diplomacy' (2023).